Synthesis of Indolones via Radical Cyclization of N‐(2‐Halogenoalkanoyl)‐Substituted Anilines

Abstract The radical reactions of N ‐(2‐halogenoalkanoyl)‐substituted anilines (anilides) of type 1 have been investigated under various conditions. Treatment of compounds 1a – 1o with Bu 3 SnH in the presence of (2,2′‐azobis(isobutyronitrile) (AIBN) afforded a mixture of the indolones (oxindoles) 2a – 2o and the reduction products 5a – 5o ( Table 1 ). In contrast, the N ‐unsubstituted anilides 1p – 1s, 1u , and 1v gave the corresponding reduction products exclusively ( Table 1 ). Similar results were obtained by treatment of 1 with Ni powder ( Table 2 ) or wth Et 3 B ( Table 3 ). Anilides with longer N ‐(phenylalkyl) chains such as 6 and 7 were inert towards radical cyclization, with the exception of N ‐benzyl‐2‐bromo‐ N ,2‐dimethylpropanamide ( 6b ), which, upon treatment with Ni powder in i‐PrOH, afforded the cyclized product 9b in low yield ( Table 4 ). Upon irradiation, the extended anilides 6, 7, 10 , and 11 yielded the corresponding dehydrobromination products exclusively ( Table 5 ).